Technical Abstract:
ABSTRACT: The objective of this experiment was to determine if feeding two levels of dietary metabolizable protein (102% vs. 119% of NRC requirements) and biological variation in feed intake during the second and third trimesters of gestation influenced subsequent production traits in primiparous heifers. Two-yr-old Angus and Simmental x Angus heifers (n = 120, initial BW = 448 ± 36 kg) had individual DMI determined using a GrowSafe feeding system. Dietary treatments were based on approximately 85% grass hay and 15% supplement. Supplements contained whole soybeans plus corn (102% MP) or dried distillers grains plus soybean meal (119% MP) and each supplement was assigned to two pens. Heifers were randomly assigned to one of three periods (P; 40 heifers/P) followed by random assignment to one of four pens (10 heifers/pen). Diets were fed at approximately 10.3 kg DM'heifer*-15*'d*-15*. After 35 d of intake measurement, heifers were placed into adjacent pens and fed their diets for an additional 50 (P1 and 2) or 82 d (P3). The next 40 heifers (P2) were placed in the facility and DMI was again determined over 35 d. Upon completion of the feeding trial, heifers were returned to the ranch, managed as a single group, and production data were measured. Level of dietary MP had no effect (P > 0.17) on calf birth weight, adjusted 205 d weight, ADG, age at weaning, cow BW at calving, proportion of cows cycling at bull turnout, or proportion of cows which conceived. Dry matter intake per unit of BW*0.75* (range = 0.057 - 0.187 kg/kg) did not affect (P > 0.17) any of the variables measured. Under the conditions of this study, feeding MP in excess of NRC recommendations during mid- to late-gestation did not enhance subsequent heifer productivity. Heifers that consumed less DM/kg BW*0.75* produced similarly to heifers that consumed more DM/kg BW*0.75*.